Pension and Postretirement Benefits (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 24, 2017 USD ($) plan	Sep. 25, 2016 USD ($)	Sep. 24, 2017 USD ($) plan	Sep. 25, 2016 USD ($)
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension and other postretirement benefit	$ (53)	$ (76)	$ (156)	$ (235)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of pension plans | plan	2		2
Components of net periodic benefit costs:
Service cost	$ 157	75	$ 470	225
Interest cost	780	813	2,341	2,431
Expected return on plan assets	(1,045)	(1,044)	(3,134)	(3,133)
Amortization of unrecognized loss (gain)	43	20	131	61
Total	(65)	(136)	(192)	(416)
Pension and Other Postretirement Benefits Cost (Reversal of Cost) [Abstract]
Pension contributions	822		1,485
Expected employer contributions during the current fiscal year	349		349
Postretirement [Member]
Components of net periodic benefit costs:
Service cost	0	4	2	14
Interest cost	28	56	82	167
Expected return on plan assets	0	0	0	0
Amortization of unrecognized loss (gain)	(16)	0	(48)	0
Total	$ 12	$ 60	$ 36	$ 181